1. Field of the Invention
The invention relates to an expansion hose for reducing the pressure pulsations and sounds associated therewith in hydraulic systems caused by the pump. Expansion hoses of this kind are used in power steering plants of motor vehicles in which the pressure hose reacts at varying operational pressures by a change of the volume of the hose by expansion and reduces thereby the pressure pulsations and the sounds originating from the pump. This reduction of the pressure pulsations and sounds depends upon the length, the cross-section and the expansion of the volume of the expansion hose. Because, however, the space available for the installation of the pressure hose is limited in a motor vehicle, it is not possible to arbitrarily select its dimensions and the result achieved is not satisfactory in many cases.
2. Description of the Related Art
In order to arrive at better results it has already become known to arrange a further inner flexible hose in an outer expansion hose. The inner flexible hose is connected at one end to the inlet side end member and ends freely with its other open end in the outer expansion hose. This may lead, however, due to the positions of the two hoses not being controllable, to damage at the inner side of the outer expansion hose which may be the cause for a defect that is not immediately recognizable. In order to achieve a further improvement, it is furthermore also known to additionally provide about at the center of the outer expansion hose a throttle member having an axial throttle through passage and which divides the outer expansion hose into two hose chambers interconnected by the throttling through passage, whereby the inner hose includes radial passages at the location of the first inlet side hose chamber. The flow resistance in the inner hose leads to a phase shift between the two hydraulic flows in the inlet side hose chamber and also due to the reverse flow of the pressurized medium from the steering side into the outlet side hose chamber, as a result of which a pulsation and sound is achieved.
The above mentioned known variants of solutions, however, do not always lead to the desired object to satisfy the highest demands regarding comfort with regard to the attenuation of sound and reduction of pulsations in a vehicle.
It is thus an object of the invention to provide an improved expansion hose for a pressurized hydraulic system such that pressure pulsations produced by the pump cannot be sensed as sound in extreme cases. It has been recognized that dividing the pressurized medium at the inlet side into a flow portion entering the annular space between the outer pressure hose and the inner hollow body and into a further flow portion entering directly into the inner hollow body, in combination with the further feature of the inner hollow body extending into the outlet side end member leads to specifically good results. According to a further preferred embodiment the outer pressure hose can be equipped additionally with an already known throttling member having axial throttle passages by means of which the pressure hose is subdivided into chambers.